Students at Dulaney Valley Senior High School today were mourning the loss of a fellow student who was killed last night after being hit by a car while attempting to cross Interstate 83 near Timonium.

The youth, Phillip Edward Cross, 14, of the first block Daria Court in Mays Chapel Village, died of massive injuries after he was struck by at least three vehicles just before 8 p.m.

The accident occurred about a half-mile from the youth's home, said State Police Trooper George B. Harrison of the Golden Ring barracks.

Trooper Harrison said young Cross and at least three other teen-agers were walking through a wooded area just west of the interstate and south of the Padonia Road interchange when they decided to cross the highway through an underground storm drain.

Instead, the trooper said, the Cross youth decided to run across the highway. His friends told him not to risk the --, but the teen-ager ran onto the shoulder and got as far as the middle of the three lanes when he was hit by a southbound 1985 Chevrolet Monte Carlo driven by Jack Edwin Guilliams, 50, of the first block of Geranium Place, Essex.

Thinking he hit an animal, Mr. Guilliams stopped on the shoulder and ran back to the scene, where he saw the youth lying in the road.

"There wasn't anything he could do for the boy," said Trooper Harrison.

The other boys ran home and told their parents.

While Mr. Guilliams stood on the shoulder, the boy was run over by two other vehicles.

Trooper Harrison said young Cross apparently was killed by the impact of the first vehicle.

He said the dead boy's uncle, a Baltimore County policeman assigned to the aviation unit, arrived at the scene and identified his nephew.

The drivers involved in the incident were not injured, and pedestrian error was given as the cause of the accident.

Baltimore County police said members of the school system's crisis intervention unit were conducting sessions today at Dulaney Valley Senior High in an attempt to relieve the grief the students will experience while mourning their friend's death.